resilience with tailored recovery time in switched …jakab/papers/2003/noc2003pre.pdfflexible...

NOC’2003 Vienna 1

Resilience with Tailored Recovery Time in Switched

Optical NetworksT. Jakab, Zs. Lakatos,

[email protected] of Telecommunications,

Budapest University of Technology and EconomicsBudapest, Hungary

NOC’2003 Vienna 2

Outline

• Motivations• Optical Channel Based Services in Switched Intelligent

Optical Networks • Potential Resilience Options for Permanent Optical

Channel Based Services• Resilience with Tailored Recovery Time • Summary and Conclusions

NOC’2003 Vienna 3

Motivations• Intelligent flexibility is required in optical

networks– to cope with traffic uncertainties, – to enable fast optical channel provisioning,– to support complex shared capacity based

resilience.• Efficient resilience schemes are of increased

importance in optical networks carrying highly concentrated traffic.

• Service differentiation is a crucial point to support different client services and improve service profitability.

NOC’2003 Vienna 4

Optical Channel Based Services

• Transport Services– Permanent optical channel service,– Soft-permanent optical channel service,– Lambda trunking service,– OVPN service.

• Service Requirements– Fast provisioning,– Differentiated services,– Enhanced service resilience.

NOC’2003 Vienna 5

Network Resilience• Dynamic application of extra network resources to limit

the impact of failures• Based on dedicated or shared network resources• Requires intelligent switching function to be supported in

nodes• Basic schemes:– 1+1 dedicated protection,– n:m shared protection,– restoration (failure state dependent dynamic

configuration of shared capacities).

NOC’2003 Vienna 6

Illustrative numerical results

• Analysis of different resilience options– Full flexibility implies restoration

• Resilience of switched OCh based services– Service oriented considerations – restoration with

tailored recovery time

NOC’2003 Vienna 7

Illustrative examples (1)Resilience in Full Flexible Networks

0%50%

100%150%200%250%300%

notprot.

optimalpathrest.

1+1

Resilience Cases

Rel

ativ

e H

op*O

Ch

Extra for resilienceWorking

0%

50%

100%

150%

200%

250%

300%

not prot.

full flex.

1+1 term.

switch.

1+1 full

flex.

optimal

path rest.

full flex.Resilience Cases

Rel

ativ

e #S

witc

h Po

rts

Extra due to resilience

Working

• Full flexible network: each capacity unit terminates on switching-capable node equipment (e.g. flex. OADM or OXC)

Comparison of link capacities Comparison of switch capacities

Extra for dedicated resilience

Savings on capacity sharing Switches

not used for resilience

NOC’2003 Vienna 8

Illustrative examples (1a - Link capacities)Resilience in Full Flexible Networks

0%50%

100%150%200%250%300%

notprot.

optimalpathrest.

1+1

Resilience Cases

Rel

ativ

e H

op*O

Ch


0%

50%

100%

150%

200%

250%

300%

not prot.

full flex.

1+1 term.

switch.

1+1 full

flex.

optimal

path rest.


Rel

ativ

e #S

witc

h Po

rts


Working






NOC’2003 Vienna 9

Illustrative examples (1a)

Link capacities for Resilience in Full Flexible Networks


Comparison of link capacities

0%50%

100%150%200%250%300%

notprot.

optimalpathrest.

1+1

Resilience Cases

Rel

ativ

e H

op*O

Ch Extra for resilience

Working Savings on capacity sharing


NOC’2003 Vienna 10

Illustrative examples (1b - Switch capacities)Resilience in Full Flexible Networks

0%50%

100%150%200%250%300%

notprot.

optimalpathrest.

1+1

Resilience Cases

Rel

ativ

e H

op*O

Ch


0%

50%

100%

150%

200%

250%

300%

not prot.

full flex.

1+1 term.

switch.

1+1 full

flex.

optimal

path rest.


Rel

ativ

e #S

witc

h Po

rts


Working







Illustrative examples (1b)

Switch capacities for Resilience in Full Flexible Networks


0%50%

100%150%200%250%300%

not prot.full flex.

1+1 term.switch.

1+1 fullflex.

optimalpath rest.full flex.Resilience Cases

Rel

ativ

e #S

witc

h Po

rts

Extra due to resilienceWorking

Comparison of switch capacitiesSwitches not used for resilience purposes


Network Resilience Service Considerations

• Different applications may need resilience with different characteristics, such as– recovery speed, or– rate of recovered capacity (partial/entire).

• Different resilient classes can be specified according to the different needs

• Aim: meet different resilience requirements on the same technical basis and lowest cost


Illustrative examples (2)Restoration with Tailored Recovery

Time

• Recovery time is assumed to be proportional with the number of active switching nodes involved in the process, and with the processing load of each active switch

• Some switches can be pre-set and fixed to speed up the recovery process

• Reduced flexibility results in less efficient capacity sharing, therefore the amount of extra resources for restoration is increasing

• The joint optimisation of different classes may reduce the penalty



TimeWorking path 1

Working path 2

SingleFailure 1

SingleFailure 2

Recovery path 2

Recovery path 1



TimeWorking path 1

Working path 2

SingleFailure 1

SingleFailure 2

Recovery path 2

Recovery path 1Pre-setswitches

Capacitysharing



TimeWorking path 1

Working path 2

SingleFailure 1

SingleFailure 2

Recovery path 2Recovery path 1Pre-set

switches

No capacitysharing



Time

Traditional restoration

1+1dedicated protection

Resource needs for networks with differentresilience options

0%

20%

40%60%

80%

100%

120%

1+1 pathprot.

single hoppath rest.

min. pathrest.

doublehop path

rest.

doubleand triplehop path

rest.

capac.opt. path

rest.

Resilience options

OC

h*ho

p

Recovery path statistics for different resilienceoptions

0.000.501.001.502.002.503.003.50

1+1 pathprot.


min. pathrest.

doublehop path

rest.


rest.

capac.opt. path

rest.

Resilience options

Ave

rage

logi

cal

hop

coun

t

spare for resilience

working


Illustrative examples (2a - Average Logical Hop Count)Restoration with Tailored Recovery Time


0%

20%

40%

60%

80%

100%

120%

1+1 pathprot.


min. pathrest.

doublehop path

rest.


rest.

capac.opt. path

rest.

Resilience options

OC

h*ho

p


0.000.501.001.502.002.503.003.50

1+1 pathprot.


min. pathrest.

doublehop path

rest.


rest.

capac.opt. path

rest.

Resilience options

Ave

rage

logi

cal

hop

coun

t


working



0.000.501.001.502.002.503.003.50

1+1 pathprot.


min. pathrest.

doublehop path

rest.


rest.

capac.opt. path

rest.

Resilience options

Ave

rage

logi

cal

hop

coun

t

Illustrative examples (2a)Restoration with Tailored Recovery Time

Average Logical Hop Count

1+1 dedicated protection

Traditional restoration

Single logical hop, receiver end

switching only

Fastest

Multiple logical hops, switching in each node via

the path

Slowest


Illustrative examples (2b - Resource Needs)Restoration with Tailored Recovery

TimeResource needs for networks with different

resilience options

0%

20%

40%

60%

80%

100%

120%

1+1 pathprot.


min. pathrest.

doublehop path

rest.


rest.

capac.opt. path

rest.

Resilience options

OC

h*ho

p


0.000.501.001.502.002.503.003.50

1+1 pathprot.


min. pathrest.

doublehop path

rest.


rest.

capac.opt. path

rest.

Resilience options

Ave

rage

logi

cal

hop

coun

t


working



0%

20%

40%

60%

80%

100%

120%

1+1 pathprot.


min. pathrest.

doublehop path

rest.


rest.

capac.opt. path

rest.Resilience options

OC

h*ho

p

Illustrative examples (2b)Restoration with Tailored Recovery Time

Resource NeedsHighest extra for

resilience(No sharing - 1+1

dedicated protection only)

Capacity optimal restoration without

recovery time specifications

Same routing without effective

capacity constraints (simplified case)

From faster to slower

spare for resilienceworking

Demand classes with different recovery time

requirements,different classifications


Summary on Restoration with Tailored Recovery Time

• Different clients and applications require different recovery times

• Applying restoration, to shorten the the recovery time some switches can be pre-set via the restoration paths

• Pre-set switches decrease de resilience capacity sharing efficiency, therefore the resilience related extra capacity increases

• Joint optimisation of multiple recovery time classes decreases this penalty


Conclusions

• Intelligent switching introduced in optical networks enables enhanced resilience schemes

• Shared capacity oriented restoration is the cost effective solution for the resilience in full flexible networks

• Demand classes of different recovery times enables service differentiation, however the joint optimisation of these classesresults in low capacity penalty

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